I don’t understand how a scan of the exterior of your ears can improve the sounds of an ‘in ear’ headphone.
Can anyone ELI5?
I’m skeptical.
I wanted to write a short explanation but this quickly became a wall of text... I'm not very knowledgeable about this but I'm going to explain it the way I understood it. I'm sure someone will correct me if I say something wrong on the internet anyway.
Every human has a unique ear shape. Sound waves that reach your ears will bounce on the shape of your external ears before reaching your eardrums. The frequency of a sound wave will change when the wave bounces in your ear. Even the size/shape of your head and other factors play a role here. This means that every person is going to experience music in a different way.
Spatial awareness is also affected by the shape of the ears. The reason we can tell if a sound is coming from above or below is because sound waves bounce in our ears in a particular way depending on the direction. Headphones (especially in-ear) usually ignore the shape of your ears and deliver audio directly to the eardrums. This means that the sound frequency will be slightly off. Usually stereo audio has horisontal spatial awareness by having different sound volume for each ear but that's far from perfect.
It's worth mentioning here that
binaural microphones exist. These are basically two microphones placed inside the ears of a doll that has a generic shape of a person. Sounds that are recorded with these will bounce inside the artificial ears which means even if you have normal headphones you'll be able to hear spatial audio. These microphones are used for ASMR stuff you can find online.
Apple introduced Spatial Audio as a way to emulate how sound is received by generic human ears. Sound sources can be placed in a virtual space and a
Head-related transfer function (HRTF) is used to compensate for headphones ignoring the shape of our ears. Apple even added head tracking into AirPods so these audio sources stay where they are if you move your head.
The problem with using binaural microphones or spacial audio with a generic HRTF is that your ears are unique. By letting your iPhone's TrueDepth camera scan your head and ears, Apple can create a personalized HRTF just for you. Spacial audio will just be more accurate than before and you will be able hear sound closer to how it would be if you had speakers playing sound all around you.
My favorite way of testing that this works is by enabling head tracked spatialized stereo and turning my head around to see if I can track where the sound is coming from in 3D.